Spot-welding electrode



March 5, 1935. BIB'URNS l,992,990

SPOT WELDING ELECTRODE Filed June`12, 1955 A TTORNE Y.

Patented Mar.' 5, 193s .UNITED STATES PATENT OFFICE.

SPOT-WELDING ELEc'rnonE mee amis, santa Monica, cam., assigner' to TheNorthrop Corporation, Inglewood, Calif., a corporation of CaliforniaApplication June 12, 1933, serial No. 675,395

16 Claims.

. My invention relates to spot-welding electrodes, and particularly toelectrodes for spot-welding material of high thermal and electricalconductivity and small cross section, such as the sheets of aluminum andits alloys which are used in aircraft construction. Y l Owing to thehigh conductivity oi materials of this class, itis necessary to useextremely high current densities in order to generate the necessaryheat,the current density used being of the order of several million amperesper square inch. Because of the small cross section oi the materials,and of the very slight difference between the plastic or weldingtemperature of the material and the point at which it actually melts, itis necessary that the welding currents be applied for extremely shortintervals of time, and also that the time be very accurately regulated.thermore, because of the relatively slight difference in conductivitybetween the welding elec trodes and the material welded, it is verydesirable to make the electrodes as massive and as of large crosssection as possible, leaving only a very small length of the electrodeoi the same diameter las the weld, and to denne the size ci the weld byone only of the welding electrodes, making the other electrode ofmaterially larger diameter,

These desiderata have led to the development -ofthe so-called depressiontype of electrode. As stated above, one electrode, which may be calledthe back electrode is dat, and of ma terially larger diameter than theweld. The opposing or iront electrode has a body of approximately thesame diameter as that ci the back i electrode with a' iiat face, fromwhich lygircjects an extremely short-tip, which may be half or less thanhalf the diameter of the body, and whose diameter determines thediameter of the weld. The face of this tip is parallel to the plane ofthe face of the rest of the electrode, and the Vprojection is usually oithe order of one one- -hundredth of an inch long.'

, The structure thus described has two purposes. ,Flrst, the proportionof the electrode which is operated at high current density is veryvbeing limited to the projection alone. lwhen a pair of flat plates tobe welded are compressed between the front andback electrodes, and thecurrent is continued for longer than'the properlwelding time, thesoftening of the materlal welded permits the projecting tip to sink intothe material, thereby -contacting an area .equal to the entire diameterof the electrode body. As the samecurrent continues to ow, this reducesSecond,

(Cl. 21S- 4) the current density to an amountinsuiiicient to cause thesoftening of the material, the melting process is arrested, and asatisfactory weld is made even though the timing may be inaccurate.Where the sheets are other than perfectly ilat, however, 'or when thefaces of the opposed electrodes are not parallel, this arrangementdefeats its own end, since the depression electrode then contacts thetilted sheet only on the edge of the tip and the edgeof the shoulder,the current density at these points rises beyond that required forsatisfactory welding, and the result is apt to be that two-holes areburnt in the work or two improperly welded spots are produced instead ofone satisfactory weld being obtained. It is extremely dimcult to 'keeplarge sheets perfectly tiet, and it iollotvs'that either a large numberci imperfect welds are made in the course of ordi-s nary production, dueto the imperfect'.v contact, or that the Work is unduly slowed. Similarresults obtain, of course, if the iront and back electrodes are notmounted in the rst instance with their faces exsctiy parallel, or wheredeections occur in the supporting structure.

The purpose ci this invention is to minimize the difdculties abovedescribed. With this end in view, some oi the objects of the inventionare: To provide an eiectl'cde'whcse contact points are seii-alining,scthat the electrode will adjust itseli to make parallel rather thanangular contact with the work; to provide a self-aiming contact pointwhich will adjust its position to the work substantially withoutfriction; to provide an elec trode wherein the alining moment is ofgreater magnitude than could be supplied-by the lever arm correspondingto the small area of the welding tip itself; and to provide an electrodewhich will operate satisfactorily with small degrees of mis-alinement,and'which yet retains the major features of advantage of the depressiontype electrode above described;

Other objects of my invention will be apparent or will be specificallypointed out in the description forming a part of this specification, butI do not limit myself to the embodiment of my invention hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring Ato the drawing:

Figure l is an elevational view of a pair of electrodes embodying myinvention, certain of the partsbeing shown in section.

Figure 2 is a similar view oi a pair of electrodes embodying theinvention in modified form.

Figure 3 is a view, partly in elevation and partly in section, and on alarger scale, of a water-cooled Considered broadly, in the electrode ofmy in*-l vention, a ball-and-socket joint is interposed between thecontacting face of the electrode and the electrode body. Preferably thecontact tip, constituting the male half of the joint, is loosely mountedin the socket, so that it is normally out of contact therewith, beingheld in this position either by its own weight or otherwise, so that itis free to aline itself to parallel contact with the work, the ballseating in the socket as the electrodev advances. There is alsopreferably provided means, in the form of a compressible collarsurrounding the area to be welded, for alining the work and theelectrode by the application of pressure through a longer lever arm thanis'offered by the diameter of the weld itself, and the body or stem ofthe contact point on the electrode which determines the diameter of theweld is provided with a conical or sloping shoulder so that slightmis-alinements of the welding face with the work do not prevent theformation of a satisfactory weld.

'Ihese principles will be better understood by reference to the variousembodiments of my invention shown in the drawing. In the embodimentshown in Figure 1 the-usual cylindrical electrode body 1 is providedwith a taper shank 2 for connection with a conventional form ofelectrode holder. In the end of the body there is formed a substantiallyhemispherical or spherically segmental recess 4, which forms the socketof the ball-and-socket joint.

Seating in and conforming with the walls of this recess is the segmentalbase5 of a separate contact point. This point is substantially ofmushroom shape, the welding face 6 being formed on the end of the shortstem 7, the stem being of slightly smaller diameter than the maximumdiameter of the segmental base. VA snap ring 9, seated in a grooveformed adjacent the rim of the recess, permits the stem to pass throughwhile retaining the base in the socket.

The cooperating upper electrode-comprises a cylindrical body 10 having ataper shank 11 for contacting the electrode holder. In this instance thecontact point 12, whose diameter is of the same order of magnitude asthat of the stem 7, is formed integrally with the electrode body, and issurrounded by a. collar 14 of rubber or other elastically compressibleinsulating material. This collar has an angular edge 15, which surroundsand projects beyond the working face of the contact tip 16. The contacttip is of the diameter of the weld to be made, is preferably not greaterin diameter than one-half the diameter of the end 12 of the electrode,and projects very slightly, usually about three to ten thousandths of aninch, from the Aend of the contact point. The shoulder 17 formed by thejunction of contact point and tip is conical, the angle of the conebeing preferably about 5. This angle is not critical, however, andv inpractice may vary from about 1 to about 15, depending upon the serviceto which the electrode is to be put.

In use the work is inserted between the electrodes, and the upperelectrode is usually the one approached to the work. It makes contactwith the work first through the edge 15 of the rubber collar, whichforces the work against the face 6 of the lower electrode and forces itsalinement with the work before the compression of the collar permits thetip 16 to touch. When suitable pressure has been applied current ispassed, forming the weld.

The steps in the formation of the normal weld are shown in Figures 6 to8 inclusive. When the current is first turned on the tip rests upon thesurface of the work 20. It appears probable that when current flrstflows the contact between the parts of the work occurs only at scatteredpoints within the area 21 between the electrodes. The current density atthese points is extremely high, and a pool 22 quickly formed where thematerial isactually liquid, bounded by areas 24, 25 where the materialis merely softened by the passing of the current and by heat conductionfrom the molten metal. This permits the tip 16 to sink into the surfaceup to the shoulder as shown in Figure 7. If the weld is properly timed,the current is cut off at the instant when the conditions shown in thislatter figure obtain.

If the current continues to flow beyond this point, the electrode sinksdeeper into the upper sheet, andas it`sinks contacts with a continuallyincreasing area, which reduces the current density and the consequentrate of heating until equilibrium is established and no furthersoftening of the metal occurs, the conditions then being substantiallyas shown in Figure 8.

Even where the self-alining electrodes are used, however, and theelectrodes are alined with the general level of the work, irregularitiesor other causes may result in a slightly angular contact between theelectrode and the work as is shown in Figure 4.

Owing to the slope of vthe conical shoulder 17, however, this does notcause the outer edge 27 to contact immediately with the work, causingburning at the shoulder 27 and the corner 29 of the tip as would be thecase with a flat shoulder.

Instead of this the positions shown in Figure 4 are assumed, the onlydifference from the normal weld being that the tip sinks slightly deeperinto the work on one side than'on the other, and if the weld be slightlyovertimed it will be oval in form as is shown in Figure 5, theover-welded rim 30 being asymmetrical with respect to the normal weldingarea 31.

In the form of the invention shown in Figure 2, a unitary back electrode35 is used having the large flat welding .face 36. The electrode isshown with a passage 37 for the circulation of cooling water. The upperelectrode 39 is provided with the usual taper shank 40 and is alsoprovided with a channel 41 for cooling water.

In this instance the upper electrode is the one which is provided withthe segmental recess 42, whichreceives the base 43 of the mushroomshaped contact point. The stem 44 of the contact point is provided witha tip 45 and sloping` shoulder similar to that of the rigidly mounted.contact point 12 in the embodiment previously Although the contactpoint is shown rmly seated in' asocket, it will be obvious that inpractice it will drop down onto the retaining ring 46.

` As the electrode is advanced to the work the' face of the tip 45 willfirst rest upon the work and assume its proper alinement, and continuedadvance of the electrode tothe work will xseat the base -in the. socket,after which kthe weld is formed as before. form of the device is mostsatisfactory where the .members to be welded are naturally flat and thepressure applied between the electrodes need not be relied -on to alinethe work with the lower electrode.

A modification of the device best suited for extremely heavy duty isillustrated in Figure 3. In this case the electrode body 50 is drilledto form the channel 51 for cooling liquid. This channel continues, atreduced diameter, into the segmental recess 52 formed in the end of theelectrode, and on into the segmental base 54 of the contact point. Inthis instance the stem 55 of the contact point is separable from thebase,

beingvheld by friction in a tapered socket 56 formed therein.

\ A compressible rubber collar 57, provided with the angularly disposededge 59 projecting beyond the face 60 of the contact stem 55, surroundsthis stem tightly, iltting 'against the ilange oi" the base 54 andforming a liquid-tight joint therewith. A, skirt or flange 6l on thecollar surrounds the end of the electrode body 50, and is held in placeby a bead 62 which rits into corresponding groove in theeiectrode body..il guard ring 64 is threaded onto the electrode body, and carries aninturned flange 6%3 which protects the shoulder 66 of the collar.

in this form'of the apparatus the contact point is held out of contactwith its socket not only by its own weight, but-also by the resiliencyof the collar and by the pressure oi the cooling liquid. Contact of theedge 59 of the collar with the work to be welded alines the contactpoint, the collar flexing at the shoulder `65, and the base 54 seatingin the recess `-522 as the eiecw trede advances. j

It will be noted that thewelding iace 60 of the contact point is in thisinstance shown y being Vconical and formed without the usual tip.

8, particularly when used on harder materials such as duralumin or otherhard alloys. This appears to be due to a swagingffect, which iscomplicated by the fact that the materials though of approximately thesame hardnesswhen cold, are heated to different degrees in the weldn ingprocess, so that a sharply defined tip and sloping shoulder are formed,as shown in the 1 gures.

Although theelectrode pairs shown in Figures 1 and 2 each comprise butone electrode .with an adjustable tip, ;it .will be obvious that theelectrodes 1 and 39 or l and 50 can be used in combination, providingadjustable tips `0n both electrodes. -vIn some services that is a verydesirable arrangement, and it is shown, for ex-n ample, in my copendingapplication entitled Welding method and apparatus, Serial No. 675,- 396,filed simultaneously with/this application.

Iclaim: 1 y ffl l. A spot-welding electrode comprising a contact pointhaving a dat face/adapted to form a parallel contact with the werk andan opposite spherically segmental face, and an electrode body a recesstherein conformed to and a engaging said segmental face.

2. A spot-welding electrode comprising a contact point having a iiat-face adapted to form a parallel contact with the work and an oppomtespherically segmental face, an electrode body y a parallel contact withthe work and an opposite spherically segmental face, an electrode bodyhaving a recess therein shaped in conformity with said segmental face,and means for retaining vsaid contact point positioned within saidrecess but out of engagement with the walls thereof, whereby approachingsaid contact to said work will rst aline the contact with the work andthen engage the segmental face contact with the recess walls.

4. A. spot-welding electrode comprising a con tact point ofmushroom-like form, having a spherically segmental base and cylindricalstem and a working face formed on the end of said stem, a body for saidelectrode'recessed to conform to said base, `and a retaining ring xed tosaid body and surrounding saidstem to retain said contact pointadjustabiy positioned in said recess.

of the 5. A spot-welding electrodecomprising a corr I tact point oimushroomniike form, having a spherically segmental basel and cylindricalstein and o, working `tace formed on the end of said stern, a body forsaid electrode recessed to con-4 ionic to base. a retaining ring xed tosaid body and surrounding stein to retain said contact point adjustahlyrpositioned in said re-z cess, and oi larger diameter "f than. saidWerktag ieee surrounding said stein for contacting the Work to saidworking face therewith.

d. il spotwelding electrode comprising a conm tact point oi`mushroom-dike form, having a spherically segmental base and cylindricalstem and a'woricing iaceiormedon the endl of said stein, a body for saidelectrode recessed to conform said base, and an annular rubber collarlafilxcd to said body and contact point for holding salti case adiustablyin said recess.

i. il spot-welding electrode comprising a con@ stem, a body for saidelectrode 'recessed to conform to said base, and a ilexiblecollarailixed to said body and said contact point for holding said baseadjustably positioned in. said recess, said collar having a compresslblrim encircling the..

working face of said contact point for alining said face with the work.l 9. InI combination, a pair of cooperating spotwelding electrodes. oneof said electrodes comprising a contact 'point connecting with the bodyof said electrode by al ball-and-socket joint, and the other of saidelectrodes having a contact point positioned to engage said firstmentioned contact point, and a compressible collar surrounding one ofsaid contact points and projecting beyond the face thereof and inalinement therewith,whereby pressure applied between said electrodes andthe work to be welded will aline said work in parallel contact with saidcontact points.

10. In combination, a conducting electrode body, a contact point havinga working face relatively small with respect to the total diameter ofsaid contact point, said contact point being adjustably mounted on saidbody to permit the alinement of said face with the work to be welded,and an annular compressible collar tightly surrounding said contactpoint and projecting beyond said working face, whereby pressing saidcollar against thework is effective to aline the contact point beforethe compression of the collar permits contact of the point with thework.

11. A spot-welding electrode comprising the combination of a contactpoint having a stem of larger diameter than the weld to be formed, aprojecting tip on said stem of the diameter of said weld, the shoulderformed by the junction of said tip and said stem being in the form of aflat cone, and a compressible collar surrounding said stem andprojecting beyond the face of said tip for pressing the work to bewelded into alinement with said face by the application of the weldingpressure. l

l2. A spot-welding electrode comprising a contact point having a stem oflarger diameter than the weld to be formed, and a projecting tip on saidstem of the diameter of said weld, the shoulder formed by the junctionof said tip and said stem being in the form of a iiat cone.

13. A spot-welding electrode comprising a contact point having a sternof larger diameter than the weld to be formed, and a projecting tip onsaid-stem of the diameter of said weld, the shoulder formed by thejunction of said tip and said stem being in the form of a cone having anangle between 1 and 15.

14. In a spot-welding electrode a contact point comprising a tip of thediameter of the projected Weld and a length short as compared to thethickness of the material to be welded, and a stem of materially largerdiameter than said tip and forming therewith a shoulder of flatlyconical form.

15. In a spot-welding electrode a contact point comprising a tip of thediameter of the projected weld and a length short as compared to thethickness of the material to be welded, and a stem of materially largerdiameter than said tip and forming therewith a shoulder disposed at anangle of approximately 5 with the working face of said tip.

16. A spot-welding electrode comprising a body having a segmental recessin one end thereof and having a passage for cooling liquid opening intosaid recess, a contact point having a base shaped to conform to saidrecess and seated therein, and a flexible collar forming a liquid-tightjoint between said contact point and said body retaining said contactpoint adjustably positioned in said recess.

BRUCE BURNS. v

